Processing of polymer dispersions by spray drying

Abstract

The invention relates to a process for the recovery of thermoplastic polymers from aqueous dispersions by spray-drying after treatment with carboxylic acid of formula I ##STR1## wherein X is a single bond, --CH 2 -- or --C 2 H 4 --, and R is --H, --OH or ##STR2##

We claim: 
     
       1. A process for the processing of a thermoplastic graft co-polymer of olefinically unsaturated monomers grafted onto a rubber by spray-drying, in which a dispersion of a thermoplastic graft polymer is treated with at least one carboxylic acid of the general formula ##STR5## in which X denotes a single bond, --CH 2  -- or --C 2  H 4  --, and R denotes --H, OH or OH ##STR6##  said dispersion prepared by means of a mixture of an alkali metal salt of a carboxylic acid and an alkali metal salt of an organic sulphonic acid as emulsifier, and the pH of the dispersion being adjusted, if required, to a value less than 7, the resulting dispersion is then subjected to spray-drying and the thermoplastic graft co-polymer, is recovered in powder form.   
     
     
       2. A process according to claim 1 wherein olefinically unsaturated monomers are styrenes, alpha-methyl styrenes, acrylonitrile, methacrylonitrile, alkyl methacrylates having 1 to 8 carbon atoms in the alkyl group, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group, vinyl chloride, vinyl acetate and vinylidene chloride, and the rubber is a diene rubber, alkyl acrylate rubber or olefin rubber.   
     
     
       3. A process according to claim 1, in which the carboxylic acid of formula (I) is a propanetricarboxylic acid, a butanetricarboxylic acid or citric acid. 
     
     
       4. A process according to claim 1, in which the carboxylic acid of formula (I) is 2-phosphono-1,2,4-butanetricarboxylic acid. 
     
     
       5. A process according to claim 1, in which the pH of the dispersion is adjusted to 3 to 4. 
     
     
       6. A polymer whenever produced by the process of claim 1. 
     
     
       7. A thermoplastic moulding material containing a polymer according to claim 6. 
     
     
       8. A process according to claim 3 in which the pH of the dispersion is adjusted to 3-4. 
     
     
       9. A process according to claim 4 in which the pH of the dispersion is adjusted to 3-4.